Process of production of n-alkyl-2-benzthiazolysulfeneimides, device for their production and method of their purification

ABSTRACT

The solution concerns a process of production of N-alkyl-2-benzthiazolylsulfeneimides by means of a reaction of 2-benzthiazolylsulfenyl chloride with an excess of a corresponding alkylamine in an anhydrous reaction medium. Removement of water and moisture from the reaction medium is ensured by azeotropic distillation of a part of the solvent. The method solves also trapping of the excess amine by extraction with water to recycle it in the process, removing of the unconverted raw material from the crude product by chemical refining with aqueous lye and extraction of by-products and pitches by elutriating the product in an organic solvent with the aim to obtain pure benzthiazolylsulfeneimide containing no less than 95% of the active substance, which can be used as a vulcanization accelerator in ruber mixtures. A device for performing this method consists of a reactor with a multiple propeller mixer on a common shaft

This application is a 371 of PCT/SK02/00006 filed Apr. 25, 2002.

TECHNICAL FIELD

The invention concerns an improved method of production ofN-alkyl-2-benzthiazolylsulfeneimides as well as an equipment for theirproduction and a method of their purification.

BACKGROUND ART

Bis-benzthiazolyl-alkyl-sulfeneimides which are represented by a generalformula (I)

where R is a C₁ to C₁₂ unbranched or branched alkyl, C₃ to C₉ cycloalkylor a substituted or unsubstituted aryl group, are known for very longand they are used in the rubber industry as promising vulcanisationaccelerators which provide for excellent operational safety of rubbermixtures, impart better resistance against reversion to the vulcanizatesand better physical properties at prevulcanization at highertemperatures, and which have excellent storage stability. Sulfeneimides,based on primary amines, do not form stable N-nitrosoamines and,therefore, they are predetermined as suitable substitutes forhygienically?? problematic sulfeneamide derivatives of secondary amines(for example, N-oxydiethylene-2-benzthiazolyl-sulfeneamide) havingcomparable scorching times and vulcanization times.

Examples of known sulfeneimide accelerators areN-cyclohexyl-2-benzthiazolyl-sulfeneimide (CBSI),N-tert-butyl-2-benzthiazolylsulfeneimide (TBSI),N-isopropyl-2-benz-thiazolylsulfeneimide as well asN-tert-octyl-2-benzthiazolylsulfeneimide. The chlorinating method ofsulfeneimide preparation is started from 2-benzthiazolylsulfenylchloride, the preparation of which (described in the U.S. Pat. No.2,257,974) consists from chlorination of 2,2′-di-benzthiazolyldisulfide(MBTS) in a nonreactive organic solvent with chlorine. The U.S. Pat. No.2,304,557 in the name of Ebelke solves the sulfenyl chloride preparationfrom 2-mercaptobenzthiazole (2-MBT) in nonreactive solvents, such asCCl₄, at reflux, or in the case of solvents which are attacked bychlorine, such as benzene, at a lower temperature. After thechlorination has been completed, the mixture is heated to boiling pointwith the aim to release the excessive halogen and the resulting HCl. Theprepared benzthiazolylsulfenyl chloride is sensitive to atmosphericmoisture.

The second step of the above given preparation of sulfeneimides is areaction of the intermediate—sulfenyl chloride—with a primary amine inthe presence of a suitable base, which may be constituted by the primaryamine itself.

The U.S. Pat. Nos. 2,321,305 and 2,321,306 in the name of Messer concernpreparation of bis- and tris-sulfeneamides by inverse dosing of sulfenylchloride into the present amine in an organic solvent. The aminehydrochloride is filtered off and the product is obtained by evaporatingsolvent from the filtrate.

In the GB patent No. 817,039 Kerrigan presents preparation of a newaccelerator, N-tert-octyl-2-benzthiazolyl-sulfeneimide, at 20 to 40° C.,where the system temperature is increasing by the heat of reaction. Inorder to trap HCl, either an excess of amine or scavengers, such aspyridine, triethylamine and the like, are used. After the reaction iscompleted, the mixture is cooled down, hydrochloride is filtered off andthe mixture is successively washed with water, 5% acetic acid, 5% NaOH,water, and it is finish dried over Na₂SO₄. The solvent CCl₄ is removedby distillation at a reduced pressure and the crude product isrecrystallized from petroleum ether.

The U.S. Pat. Nos. 2,873,277 and 2,889,331 in the name of Sundholmconcern the preparation of N-alkyl- aN-cycloalkyl-bis(2-benzthiazolylsulfene)amides (TBSI, CBSI and the like)by a reaction of the corresponding amine with sulfenyl chloride at amole ratio of 3:2 and at a temperature in the range of −40 to +50° C.;the dosing method (concurrent, inverse or direct) influences quality ofthe product. After the reaction is completed, amine hydrochloride isfiltered off, the product is obtained by evaporating solvent from thefiltrate, and it may be recrystallized from ligroin.

N. K. Sundholm (Ind. Eng. Chem. 52, 239, 1960) states that the productquality is improved by lower reaction temperatures (−10° C. and lower)and by quick direct dosing. If adding inversely a small amount ofsulfenyl chloride into the reactive amine, the reaction may develop inthe direction to monosulfeneamide, where neither a temperature loweringto −20° C. will help.

The U.S. Pat. No. 478,010 in the name of Chitrina et al. concerns amethod, how to obtainN-cyclohexane-dienyl-1,4-bis-(2-benzthiazolyl)-sulfeneamide by directdosing of unsaturated 1,4-cyclohexanedienylamine into sulfenyl chlorideat a molar ratio of 2:1 at a temperature of −15 to −5° C. with asubsequent increase of temperature to 25 to 30° C. in the presence of atertiary amine as an HCl scavenger.

In the above mentioned patent publications about sulfeneimidepreparation by a chlorinating method, it is required to use dry oranhydrous solvents, respectively. Alternative methods of production ofN-alkyl- and N-cycloalkyl-2-benzthiazolylsulfeneimides from thecorresponding monosulfeneamides by means of a reaction with organicanhydrides are described in the U.S. Pat. Nos. 2,860,142, 3,875,177 and5,840,908, and by means of a reaction with strong mineral acids inanhydrous hydrocarbon medium in WO 92/05218, WO 99 58526 and EP 0 574369.

In EP 0 529 449, Sicheneder describes a promising process of preparationof bis-benzthiazolyl-alkylsulfeneimides, such as TBSI, by a reaction ofalkylamines (without proton at the α-carbon) with a substituted 2-MBT inthe presence of oxygen or oxygen containing gas, copper or coppercompounds as a catalyst in an inert organic solvent.

Although in the older references, concerning this problem, thesecompounds are termed bis(sulfeneamides), it is chemically more correctto term them sulfeneimides.

The object of the method according to the present invention is toeliminate the necessity of removing the amine hydrochloride byfiltration, crystallization from petroleum ether, as well as to obtainthe final product of better quality and with higher yield.

DISCLOSURE OF INVENTION

The above given object can be achieved by a method of production ofN-alkyl-2-benthiazolyl-sulfeneimides of the general formula I

where R is a C₁ to C₁₂ unbranched or branched alkyl, C₃ to C₉cycloalkyl,

by means of a reaction of 2-benzthiazolylsulfenyl chloride, anintermediate prepared from 2,2′-dibenzthiazolyl disulfide or2-mercaptobenzthiazole using chlorine in the presence of an inertsolvent, with an excess of a corresponding alkylamine in an inertreaction medium, according to the present invention. The nature of theinvention consists in that the reaction with sulfenyl chloride isperformed using a 10 to 100% excess of the concentrated alkylamine,compared with the theoretical amount, i. e. 3.3 to 6 equivalents ofalkylamine per 2 equivalents of sulfenyl chloride as required by theory,and moisture of the solvent, raw material, equipment as well as theresidue of not isolated alkylamine are removed by azeotropicdistillation of a part (15% at most) of the solvent, possibly at areduced pressure. The primary amine which is present in an excess servesmutually as a scavenger for the arising acid.

The free amine together with alkylammonium chloride from the reactionmixture are trapped by extraction using water or diluted acid,respectively, and by gravitational phase separation, from which amine isregenerated by distillation after a reaction with aqueous NaOH.

Condensation of benzthiazolylsulfenyl chloride with alkylamine is aheterogeneous reaction accompanied with reaction heat generation, andtherefore, an important part of the process is an equipment which allowsintensive mixing and conducting the reaction heat away duringcondensation. It is preferred to perform it in an equipment according tothe present invention, the nature of which consists in that it comprisesa reactor with multiple propeller mixers on a common shaft. The reactorconsists of a vessel in which propeller mixers are arranged on a commonshaft, and of a lid. Individual levels?? of the propeller mixers areoriented opposite one another. The shaft is supported at the bottombearing. A cooling coil is arranged in the reactor. In this way therequired intensive mixing and cooling in the decisive technological nodeis ensured.

The solvent (a part of it or as a whole) is removed from the reactionsystem by azeotropic distillation with water at a reduced pressure andat a temperature not greater than 50° C. In order to remove thedisulfide which has not reacted, aqueous sodium hydroxide is added at atemperature of 20 to 50° C. Chemical refining by the lye is performedbefore or during thickening the reaction mixture, and the sulfeneimideis separated from the solution containing impurities by filtration. Thecrude (not purified) product itself can already be used as a rubberaccelerator.

The invention further concerns a method of purification of the crudeproduct N-alkyl-2-benzthiazolylsulfeneimide, the nature of whichconsists in that the crude product is elutriated at a temperature of 10to 50° C. during 0.5 to 2 h in a polar organic solvent, selected from agroup comprising acetone, isopropanol, ethanol, their mixtures orpossibly azeotropic mixtures with water, and the pure, insolublesulfeneimide is separated from the solution which contains dissolvedimpurities by filtration.

Alternatively, aqueous suspension of the crude product is mixed at atemperature of 10 to 50° C. during 0.5 to 2 h in a nonpolar organicsolvent, selected from a group comprising alkanes, cycloalkanes,aromates and their mixtures, and the pure, insoluble sulfeneimide isseparated from the aqueous-organic emulsion which contains dissolvedimpurities by filtration.

After the solvent has been evaporated, the crude product is notcrystallized from nonpolar solvents as before, but it is refined with anaqueous lye, while the by-products of the reaction are extracted with asuitable organic solvent which may consists of the solvent used in theprocess. There are certain cases, where it is possible to omitcompletely the chemical refining by a lye, and to refine the crudesulfeneimide by mixing it in a polar organic solvent, preferably inalcohol or acetone.

The advantage of the method according to the present invention consistsin that, contrary to present procedures, the amine hydrochloride is notremoved from the thus prepared reaction mixture by filtration, but it iswashed out with water. The crude product need not to be crystallizedfrom petroleum ether, and moreover, the method according to the presentinvention leads to better quality and to higher yield of sulfeneimide.

BRIEF DESCRIPTION OF DRAWINGS

The equipment according to the present invention is shown in detail inthe attached FIGURE.

EXAMPLES OF EMBODIMENTS

The following examples explain the invention in more detail, but they donot limit the scope of the invention.

Example 1 Preparation of N-tert-butyl-2-benzthiazolylsulfeneimide (TBSI)in toluene

Chlorination of 2,2′-dibenzthiazolyl disulfide:

60.0 g (0.1742 mol) of 2,2′-dibenzthiazolyldisulfide (commerciallyavailable Altax containing 96.51% of the active substance according toHPLC) and 750 ml of toluene were added to a 2 I three-necked flask. 75ml of the solvent were distilled off under stirring, and the solutionwas cooled down to 25° C. Dry chlorine (12.97 g, 0.183 mol) was passedinto the mixed suspension during 60 minutes, and the reaction mixturewas mixed another 0.5 h at 25° C.

Condensation

A solution of 2-benzthiazolylsulfenyl chloride was cooled down to 0° C.,and 45 g (0.61 mol) of concentrated tert-butylamine were added to itfrom a dropping funnel within 100 minutes at 0° C. After the amineadding had been completed, the mixture was mixed for 1.5 h understirring and then the cooling was removed within 0.5 h.

Extraction of tert-butylamine

From the reaction mixture containing TBSI alkylamine hydrochloride andfree tert-butylamine were isolated by multiple extraction with water andgravitational discharge of the aqueous phases.

Isolation of the Crude Product

To the extracted reaction mixture 800 ml of water were added and thesolvent was azeotropically distilled off at a reduced pressure in such away, that the temperature in the apparatus did not exceed 50° C. Thecrude product (TBSI) was obtained from the aqueous phase by filtration.After completion of drying 71.7 g, i. e. 102% of the theoretical yield,of the crude product containing up to 90% of the active substance, wasobtained; already this crude (not refined) product can be used as arubber accelerator.

Crude Product Refining

The wet filter cake was physically refined during 1 h by elutriation ina 7-fold amount of technical isopropanol at ambient temperature. Afterfiltration and drying 62.36 g of the refined product was obtained havinga 96.9% purity according to HPLC, the yield being 88.7% of thetheoretical value.

Example 2

Chlorination of disulfide, condensation with tert-butylamine andextraction of tert-butylamine were performed using the procedure fromExample 1.

Crude Product Isolation

To the extracted reaction mixture 800 ml of water and 82 g of 18%aqueous NaOH were added. Chemical refining directed at decomposition ofthe disulfide which had not reacted took place during 2 h of azeotropicdistillation of toluene at a reduced pressure and under stirring at atemperature under 50° C. The crude product was filtered off from theaqueous phase and washed with water.

Crude Product Refining

The filter cake obtained was physically refined during 1 h byelutriation in a 3-fold amount of acetone at ambient temperature. Afterfiltration and drying 60.74 g of the refined product were obtainedhaving a 98.3% purity according to HPLC (yield 86.4% of the theoreticalvalue).

Example 3

Suspension of the crude TBSI in water (obtained after azeotropicdistillation of toluene) was prepared by the procedure, given in Example2.

To the crude product in water, a half amount of toluene, referred to theweight of the crude product, was added and the mixture was physicallyrefined by mixing for 1 h at 50° C. After cooling down, filtration anddrying 60.7 g of the refined product were obtained having 96.97% purityaccording to HPLC (yield 86.3% of theoretical value).

Example 4

Suspension of the crude TBSI in water (obtained after azeotropicdistillation of toluene) was prepared by the procedure, given in Example2.

Double amount of cyclohexane, referred to the weight of the crudeproduct, was added to it and the mixture was physically refined bymixing for 1 h at 50° C. After cooling down, filtration and drying 63.7g of the refined product were obtained having 96.33% purity according toHPLC (yield 90.6% of the theoretical value).

Example 5 Preparation of N-tert-butyl-2-benzthiazolylsulfeneimide (TBSI)in cyclohexane

Chlorination

20 g (0.058 mol) of 2,2′-dibenzthiazolyldisulfide (commerciallyavailable Altax containing 96.51% of the active substance according toHPLC) was mixed with 320 ml of cyclohexane in a 500 ml three-neckedflask and 30 ml of the solvent were distilled off. 4.3 g (0.061 mol) ofchlorine were added within 60 minutes in a temperature range of 40 to45° C., the mixture was heated to 75° C., and blown through withnitrogen.

Condensation

The reaction mixture was cooled down to 10° C., 23.4 g (0.32 mol) oftert-butylamine were added during 120 minutes, and it was stirred 60minutes at a reaction temperature.

Refining

After water and NaOH solution had been added, 60% of the solvent weredistilled off from the reaction mixture at a reduced pressure and at atemperature not greater than 50° C. After cooling down, filtration andwashing with water 19.6 g of the product were obtained having a 97%purity according to HPLC (yield 83.8% of the theoretical value).

Example 6

Chlorination of disulfide and condensation with tert-butylamine were thesame as in Example 5.

Refining

After the condensation had been completed, 150 ml of water were added tothe flask and the aqueous solution of amine chloride was separated. Theorganic phase in the flask was washed with 50 ml of water (or dilutedacid) two more times and finally 200 ml of water were added and theorganic solvent was distilled off completely at a reduced pressure. Thecrude product was filtered off and refined by mixing for 60 minutes in a3-fold amount of acetone. After filtration 19.45 g of the product (yield83%) having 97.6% purity according to HPLC were obtained.

Example 7 Preparation of N-cyclohexyl-2-benzthiazolylsulfeneimide (CBSI)in cyclohexane

Chlorination of the disulfide was the same as in Example 5.

Condensation

The reaction mixture was cooled down to 10° C., 31.7 g (0.32 mol) ofcyclohexylamine were added during 120 minutes, and it was stirred 60minutes at a reaction temperature.

Refining of the reaction mixture and product isolation were the same asin Example 5.

After drying the filter cake 17.9 g of the product having 98.5% purityaccording to HPLC (72% of the theoretical yield) were obtained.

Example 8 Preparation of TBSI in a Reactor with a Multiple PropellerMixer on a Common Shaft

Chlorination

Benzthiazolylsulfenyl chloride was prepared from 700 kg of 98%commercially available Altax (2.063 kmol) in 8750 1 of a solvent and 150kg chlorine.

Condensation

The solution of 2-benzthiazolylsulfenyl chloride was poured into thevessel (1) of a reactor (FIG. 1) with a lid (2), equipped with propellermixers (4) on a common shaft (3). It was cooled down to 5° C. and within120 minutes 604 kg (8.25 kmol) of concentrated tert-butylamine weredosed to it from a volumetric flask at a temperature lower than 15° C.After the amine dosing had been completed, the mixture was mixed for 1 hwith cooling (the reactor was equipped with a cooling box) and anotherhour without cooling.

Crude Product Isolation

After extraction with water water was added to the solution of crudeTBSI in an organic solvent and the solvent was distilled offazeotropically at a reduced pressure in such a way, that the temperaturein the apparatus did not exceed 50° C. The crude product was obtainedfrom the aqueous phase by filtration. It contained 89% of the activesubstance (after drying).

Crude Product Refining

The filter cake from the previous filtration was refined during 1 h byelutriation in 5800 1 of technical azeotropic isopropanol at ambienttemperature. After filtration and drying 725 kg of the refined productwas obtained having a 99% purity according to HPLC, the yield being87.06% of the theoretical value.

1. A method for the production of N-alkyl-2-benzthiazolyl-sulfeneimidesof the formula I

where R is selected from the group consisting of a C₁ to C₁₂ unbranchedor branched alkyl and a C₃ to C₉ cycloalkyl group, the method comprisingreacting a 2-benzthiazolylsulfenyl chloride with an excess of acorresponding alkylamine in an inert solvent reaction medium, whereinthe reaction of the sulfenyl chloride with the corresponding alkylamineis performed at a temperature of from +5 to +15° C. using a 10 to 100%excess of the alkylamine compared with a theoretical amount, removingmoisture of equipment, solvent, and raw material by distilling off apart of the solvent by azeotropic distillation at an atmospheric orreduced pressure, and removing disulfide which has not reacted by addingaqueous sodium hydroxide at a temperature of 20 to 50° C., whileseparating the sulfeneimide by filtration.
 2. A method according toclaim 1, wherein the reaction of the sulfenyl chloride with thecorresponding alkylamine is performed with an excess of 3.5 to 4equivalents of amine per 2 equivalents of sulfenyl chloride.
 3. A methodaccording to claim 1, wherein alkylammonium chloride and alkylamine areisolated from the reaction mixture by extraction with water or dilutedacid and subsequent separation of phases.
 4. A method according to claim1, wherein the solvent is removed by distilling it off using azeotropicdistillation in the presence of water, at a reduced pressure and at atemperature no greater than 50° C.
 5. A method according to claim 1,additionally comprising purification of crude productN-alkyl-2-benzthiazoylsulfenemide by elutriating crude product for 0.5to 2 hours at a temperature of 10 to 50° C. in a suitable polar organicsolvent or in its azeotropic mixture with water, and subsequentlyseparating the sulfeneimide by filtration.
 6. A method according toclaim 1, additionally comprising purification of crude productN-alkyl-2-benzthiazoylsulfenemide by mixing an aqueous suspension of thecrude product with a suitable nonpolar organic solvent or with a mixtureof such organic solvents, and mixing the resulting mixture for 0.5 to 2hours at a temperature of 10 to 50° C. and subsequently separating thesulfeneimide by filtration.
 7. A method according to claim 2, whereinalkylammonium chloride and alkylamine are isolated from the reactionmixture by extraction with water or diluted acid and subsequentseparation of the phases.
 8. A method according to claim 2, wherein thesolvent is removed by distilling it off using azetropic distillation inthe presence of water, at a reduced pressure and at a temperature nogreater than 50° C.
 9. A method according to claim 3, wherein thesolvent is removed by distilling it off using azetropic distillation inthe presence of water, at a reduced pressure and at a temperature nogreater than 50° C.
 10. A method according to claim 2, additionallycomprising purification of crude productN-alkyl-2-benzthiazoylsulfenemide by elutriating crude product for 0.5to 2 hours at a temperature of 10 to 50° C. in a suitable polar organicsolvent or in its azetropic mixture with water, and subsequentlyseparating the sulfeneimide by filtration.
 11. A method according toclaim 3, additionally comprising purification of crude productN-alkyl-2-benzthiazoylsulfenemide by elutriating crude product for 0.5to 2 hours at a temperature of 10 to 50° C. in a suitable polar organicsolvent or in its azetropic mixture with water, and subsequentlyseparating the sulfeneimide by filtration.
 12. A method according toclaim 4, additionally comprising purification of crude productN-alkyl-2-benzthiazoylsulfenemide by elutriating crude product for 0.5to 2 hours at a temperature of 10 to 50° C. in a suitable polar organicsolvent or in its azetropic mixture with water, and subsequentlyseparating the sulfeneimide by filtration.
 13. A method according toclaim 2, additionally comprising purification of crude productN-alkyl-2-benzthiazoylsulfenemide by mixing an aqueous suspension of thecrude product with a suitable nonpolar organic solvent or with a mixtureof such organic solvents, and mixing the resulting mixture for 0.5 to 2hours at a temperature of 10 to 50° C. and subsequently separating thesulfeneimide by filtration.
 14. A method according to claim 3,additionally comprising purification of crude productN-alkyl-2-benzthiazoylsulfenemide by mixing an aqueous suspension of thecrude product with a suitable nonpolar organic solvent or with a mixtureof such organic solvents, and mixing the resulting mixture for 0.5 to 2hours at a temperature of 10 to 50° C. and subsequently separating thesulfeneimide by filtration.
 15. A according to claim 4, additionallycomprising purification of crude productN-alkyl-2-benzthiazoylsulfenemide by mixing an aqueous suspension of thecrude product with a suitable nonpolar organic solvent or with a mixtureof such organic solvents, and mixing the resulting mixture for 0.5 to 2hours at a temperature of 10 to 50° C. and subsequently separating thesulfeneimide by filtration.